Multilayer material based on active lithium, method of preparation and applications in electrochemical generators

ABSTRACT

A method for preparing a multilayer material based on active lithium, by depositing a film of active lithium on a protective layer at a sufficient speed so that substantially no oxidation of the lithium occurs, and/or during a sufficient time for the adhesion of the lithium to develop after contact with the protective layer. The multilayer material, when incorporated in an electrochemical battery as an anode, has excellent impedance stability and no formation of dendrites during the cycling. Batteries where the anode is the multilayer material are particularly efficient in terms of their coulomb efficiency.

FIELD OF THE INVENTION

The present invention relates to a method for preparing a multilayermaterial based on active lithium, a method for its preparation, and itsuse in electrochemical batteries.

RELATED ART

Lithium metal batteries in which the electrolyte is a polymerelectrolyte have the advantage of supplying an energy density by weightand volume that is higher than that of Li-ion batteries, thanks to thecapacitance of the lithium metal anode which is 3700 mAh/g. This valueis 10 times higher than that of an anode based on graphite (LiC₆) or 20times higher than that of an anode of the titanium spinel (Li₄Ti₅O₁₂)type.

On the other hand, during the charging of high current lithiumbatteries, in which the lithium is electrodeposited, a potentialformation of dendrites on the lithium surface may occur fairly rapidlyafter a few cycles of use. These dendrites may perforate the separator(in which the electrolyte is impregnated) and touch the cathode.

One solution to this problem of instability is proposed in U.S. Pat. No.6,214,061. It consists in protecting a film of lithium forming the anodeof a battery by a protective layer consisting of a vitreousion-conducting material, for example glass or a lithium phosphorusoxynitride, designated by LIPON. The protective layer is deposited on asubstrate, the lithium layer is then deposited on the protective layer,and a current collector is finally deposited on the lithium layer.

The protective layer and the lithium layer are deposited by cathodesputtering or by vapor deposition. This technique yields good results.However, it requires operation under vacuum for the deposition of theprotective layer and of the lithium layer, demanding more complicatedand more costly devices at the industrial level.

The use of a thin film of lithium is important in lithium metal polymerbatteries, because it serves to optimize the excess lithium, bycomparison with the capacitance of the cathode.

The technology for obtaining thin films of lithium metal by laminationis described in CA-A-2 099 524 and CA-A-2 099 526 in the name ofHydro-Quebec.

CA-A-2 099 524 describes a method for laminating a lithium strip forobtaining a lithium film between 10 and 100 μm thick. This method ischaracterized by the fact that at the discharge end of the roll mill andafter a single passage, in the presence of a lubricant, the roll millfilm remains adhering to the surface of one of the working rolls up to agiven point on a portion of the circumference of this roll beyond themeeting point of the two rolls. Although the film obtained thereby canbe used in an electrochemical generator, it has a passivation layer witha non-negligible thickness.

CA-A-2 099 526 describes additives for lubricants usable in thelamination of lithium strips in thin films, which improves theirperformance. These additives are represented by the general formulaL-A-B where L is a hydrocarbon radical acting as a lubricant segment, Bdenotes an oligomer segment serving as a solvate segment for the metalsalts, and A is a chemical bond joining the hydrocarbon radical to theoligomer segment.

SUMMARY

It is an object of the present invention to propose a method forpreparing electrochemical batteries which have an anode whereof theactive material is a thin film of lithium, which can be implemented atatmospheric pressure, that is in the most convenient industrialconditions, and which yields batteries in which said lithium filmadheres perfectly to the elements of the battery adjacent to it and doesnot form dendrites during operation.

This is why the present invention relates to a method for preparing amultilayer comprising at least one film of lithium, the multilayerobtained, and its use as an anode in an electrochemical battery.

The inventive method is suitable for preparing a multilayer materialcomprising at least one layer of active lithium, and it is characterizedin that it comprises a step of depositing a film of active lithium on aprotective layer at a sufficient speed so that substantially nooxidation of the lithium occurs, and/or during a sufficient time for theadhesion of the lithium to develop after contact with the protectivelayer.

The multilayer material according to the invention comprises at leastone layer of active lithium which carries a protective layer on at leastone of its surfaces, said protective layer consisting or consistingessentially of an ion-conducting material.

A multilayer material of the invention, when incorporated in anelectrochemical battery as an anode, has excellent impedance stability,with no formation of dendrites during cycling.

The batteries of which the anode comprise a multilayer material of theinvention are particularly efficient in terms of their coulombefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B: show the variation in thickness of a passivation filmof lithium (E, in Å) on the y-axis, as a function of exposure time in adry air atmosphere (T, in seconds) on the x-axis, for a lithium filmobtained according to the invention; FIG. 1A is an enlarged view of thezone T=0 to 1 of FIG. 1B.

FIG. 2: shows the method for applying the protective film to thelithium, which serves to maintain the thickness of the passivation layerof lithium constant over time; the curves E (in Å) as a function of T(in seconds) show the variation in thickness of the passivation layer,before (left-hand curve) and after the deposition of two protectivelayers (right-hand curve); Li denotes a film of standard lithium, Li*denotes a film of active lithium; P denotes the protective material(glass or ceramic); No. 1 and No. 2 respectively denote the 1^(st) andthe 2^(nd) step of the process.

GENERAL DESCRIPTION OF THE INVENTION

A first object of the invention relates to a method for preparing amultilayer material which comprises at least one layer of activelithium, said method comprising a step of depositing a film of activelithium on a protective layer at a sufficient speed so thatsubstantially no oxidation of the lithium occurs, and/or during asufficient time for the adhesion of the lithium to develop after contactwith the protective layer.

The layer of active lithium consists or consists essentially of lithiumwhich has a degree of purity higher than 99%, or of a lithium alloycomprising less than 3000 ppm of impurities. Such a layer has goodadhesion properties.

In one embodiment, the layer of active lithium carries on one or each ofits surfaces, a passivation layer which is such that the ratio“thickness of the passivation layer”/“thickness of the layer of activelithium” is between 2.105 and 1.10⁻³.

In another embodiment, the thickness of the passivation layer is zero.

The passivation layer comprises at least one lithium compound from thegroup consisting of Li₂O, Li₂CO₃, LiOH, and Li₂S₂O₄. Li₂O, Li₂CO₃ andLiOH are formed in a dry atmosphere, Li₂S₂O₄ is formed in the presenceof SO₂.

It is particularly preferred to effect the deposition of the film ofactive lithium on the protective layer by lamination. The conditions forcarrying out a lithium deposition on a support layer by lamination,especially the additives used, in particular the lubricants, aredescribed in CA-A-2 099 524 and CA-A-2 099 526.

When the multilayer material is intended for use as a two-sided anode ina battery, a protective layer is deposited on each of the surfaces ofthe film of lithium, the two protective layers consisting or consistingessentially of an ion-conducting material.

When the multilayer material is intended for use as a one-sided anode ina battery, the film of active lithium is deposited on a protective layerconsisting or consisting essentially of an ion-conducting material. Itis advantageous to deposit, on the other surface of the film of activelithium, a protective layer consisting or consisting essentially of anelectron conducting material which may act as a current collector forthe anode.

The deposition of the lithium layer by lamination allows operation atatmospheric pressure. The multilayer material is preferably prepared ina dry air atmosphere, in an anhydrous chamber characterized by a dewpoint between −45 and 55° C., which is between 0.7 and 2.2%, andpreferably at −50° C. at 1.3% relative humidity.

A protective layer may be deposited in 1 to 15 seconds.

When the multilayer material comprises two protective layers on eitherside of the layer of active lithium, the second protective layer may bedeposited on the film of active lithium at the same time as the firstprotective layer is deposited on the other free surface of the lithiumfilm. The second layer may also be deposited after the deposition of thefirst layer, preferably less than 15 seconds after.

The material used to form a protective layer has an ion conductionhigher than 10⁻⁴S.cm², and is selected from ceramics, glasses, polymers,and mixtures thereof.

An ion-conducting protective layer may comprise at least two sublayers,consisting or consisting essentially of, independently of one another, amaterial which has an ion conduction higher than 10⁻⁴S.cm², and which isselected from ceramics, glasses, and polymers optionally containing aceramic filler.

A protective layer of ceramic advantageously consists or consistsessentially of a ceramic of the nonstoichiometric lithium phosphorusoxynitride type. This type of ceramic is generally designated by thename LIPON. In the context of the present invention, the compoundLi_(3.3)PO_(3.9)N_(0.17) and similar compounds are preferably used. Adetailed presentation of LIPON compounds of their use, particularly forthe preparation of thin films for all-solid batteries, is provided in“Micro Power Sources”, K. Zaghib and S. Surampudi, Proceedings Volume2000-03, pp. 70 to 79, published by The Electrochemical Society.

A LIPON ceramic layer may be deposited on a substrate by cathodesputtering, laser or plasma ablation, for example from a Li₃PO₄ target.The substrate for the deposition of the protective film may be a film ofpropylene or of a PP-PE-PP copolymer serving as a separator in thegenerator. The substrate may further be a ½ cell and consists of acollector, a cathode and an electrolyte, the LIPON layer being depositedon the electrolyte layer. The protective layer may also be formed on anysubstrate carrying a film of PP, said film being removable by peelingafter formation of the protective layer, and deposition of the lithiumfilm on the protective layer.

A protective layer may further consist or consists essentially of glass.

A protective layer consisting or consisting essentially of a ceramic orof a glass preferably has a thickness equal to or lower than 1 μm.

A protective layer may consist or consists essentially of a solution ofan ionic compound in a polymer or of a polymer carrying ionic groups.The polymer may further contain a ceramic.

A protective layer of the polymer type preferably has a thickness of 1to 100 μm.

For the protective layer consisting or consisting essentially of apolymer to have good mechanical strength, it is preferable to selecteither a high molecular weight polymer which has an intrinsic mechanicalstrength, or a polymer which has crosslinkable groups and to which acrosslinkage imparts the mechanical strength. Polyethers or polyvinylsare particularly preferred.

Polymers usable as a material constituting a protective layer may beselected from polymers with 3 branches and polymers with 4 branches.

Polymer with 3 branches means a polymer having 3 branches in the form ofa three-branched comb, like those described in “Relationship betweenStructural Factor of Gel Electrolyte and Characteristics of Electrolyteand Lithium-ion Polymer Battery Performances”, by Hiroe Nakagawa et al,The 44^(th) Symposium in Japan, Nov. 4-6, 2003, abstract 3D26. The 3substantially parallel branches of these polymers are preferably fixedto the center and to the two ends of a small skeleton, preferablycomprising 3 atoms, more particularly 3 carbon atoms in the chain. Inthe case of a chain with 3 carbon atoms, each of the atoms is connectedto a branch.

Among these polymers with 3 branches, those which have an averagemolecular weight (M_(W)) of between 1,000 and 1,000,000 are preferred,more particularly those having an average molecular weight of between5,000 and 100,000.

Polymer with four branches means a polymer in the form of afour-branched comb. WO-03/063287 describes a preferred family ofpolymers with four branches. The 4 substantial parallel branches ofthese polymers are fixed respectively between the two ends (preferablysymmetrically on the chain) and at the two ends of a small chainpreferably having 4 atoms, which are preferably 4 carbon atoms. In thecase of a chain having 4 carbon atoms, each atom is connected to abranch.

Among these four-branched polymers, those having hybrid terminal groupsare preferred, more particularly hybrid acrylate (preferablymethacrylate) and alkoxy (preferably alkoxy with 1 to 8 carbon atoms, inparticular methoxy or ethoxy), or vinyl groups, at least one branch ofsaid four-branched polymer (and preferably at least two branches) beingcapable of giving rise to a crosslinkage.

Another family of polymers with four branches, useful for the presentinvention, is described in columns 1 and 2 of U.S. Pat. No. 6,190,804.This document is incorporated by reference in the present application.

The polymer is preferably a star polyether which has at least fourbranches having terminal groups containing the following functions:acrylate or methacrylate and alkoxy, allyloxy and/or vinyloxy, at leastone, and preferably at least two of these functions being active forcrosslinkage. It has a voltage stability much higher than 4.

An example of a polyether with 4 branches is a tetrafunctional polymerpreferably having a high molecular weight and having the formula (1):

where:

-   -   R¹ and R² each represent a hydrogen atom or a lower alkyl        (preferably having 1 to 7 carbon atoms);    -   R³ represents a hydrogen atom or a methyl group;    -   m and n each represent a whole number higher than or equal to 0;    -   in each high molecular weight chain, m+n>35;    -   each of the groups R¹, R², R³ and each of the parameters m and n        may be identical or different in the 4 high molecular weight        chains.

Among these polymers with four branches, those which have an averagemolecular weight between 1,000 and 1,000,000, preferably between 5,000and 100,000, are particularly advantageous.

Vinyl polymers of the ethylene glycol (EG) type, and more particularlythose described in EP-A-1 249 461 (DKS), are also advantageous asprotective materials, in particular those having an average molecularweight between 600 and 2,500.

Polymers of this family may advantageously be obtained by reactingethylene oxide and 2,3-epoxy-1-propanol with HO—(—CH₂CH₂O—)₄—H) or byreacting 2,3-epoxy-1-propanol with ethylene glycol. This step isfollowed by the grafting of polymerizable and/or nonpolymerizablefunctional groups at each end of the skeleton and of the side chains ofthe polymer. Compounds having one or more groups carrying an activehydrogen and alkoxy groups may also be used in the form of monomerswhich are crosslinked in situ, during the preparation of the protectivelayer.

The hydroxyl group is an example of a group carrying an active hydrogen.

Compounds having 1 to 5 hydroxyl groups are preferred. Themonomethylether of triethyleneglycol, ethyleneglycol, glycerin,diglycerin, pentaerythritol and derivatives thereof are specificexamples of compounds having one or more groups carrying an activehydrogen.

CH₃ONa, t-BuOK and derivatives thereof are specific examples ofprecursor alkoxides of alkoxy groups.

The polyether polymers used as a material for the protective layer havea structural unit represented by the formula (1) and the structural unitrepresented by the formula (2) and/or the structural unit represented bythe formula (3). The number of units having formula (1) in a molecule isbetween 1 and 22,800, preferably between 5 and 11,400, and moreparticularly between 10 and 5,700. The total number of units havingformula (2) and/or formula (3) is between 1 and 13,600, preferablybetween 5 and 6,800, and more preferably between 10 and 3,400.

(Meth)acrylate groups, allyl groups and vinyl groups are examples ofpolymerizable functional groups grafted at each molecular end. Alkylgroups and functional groups comprising boron atoms are examples ofnonpolymerizable functional groups. Among alkyl groups, alkyl groupshaving 1 to 6 carbon atoms are preferred, particularly those having 1 to4 carbon atoms, and more particularly the methyl group.

Examples of functional groups comprising boron atoms include thosepresented by the following formulas (4) or (5)

The groups R¹¹ and R¹² in formula (4) and the groups R²¹, R²² and R²³ inthe formula (5) may be identical or different, and alkyl, alkoxy, aryl,alkenyl, alkynyl, aralkyl, cycloalkyl, cyano, hydroxyl, formyl, aryloxy,alkylthio, arylthio, acyloxy, sulfonyloxy, amino, alkylamino, arylamino,carbonamino, oxysulfonylamino, sulfonamide, oxycabonylamino, ureid,acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, oxysulfonyl,sulfamoyle, carboxylate, sulfonate or phosphonate group, a heterocyclicgroup, or a —B(R^(a))(R^(b)), —OB(R^(a))(R^(b)) orOSi(R^(a))(R^(b))(R^(c)) group in which (R^(a)), (R^(b)) and (R^(c))each represent a hydrogen, a halogen, an alkyl, alkoxy, aryl, alkenyl,alkynyl, aralkyl, cycloalkyl, cyano, hydroxyl, formyl, aryloxy,alkylthio, arylthio, acyloxy, sulfonamide, oxycarbonylamino, ureid,acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, oxysulfonyl,sulfamoyle, carboxylate, sulfonate, phosphonate, heterocyclic group orderivatives thereof. R¹¹, and R¹² in the formula (4) and R²¹ and R²²,R²³ in the formula (5) may be joined together to form a ring, and thering may have substitutes. Each group may also be substituted bysubstitutable groups. X⁺ in the formula (5) represents an alkali metalion, preferably a lithium ion.

The ends of the molecular chains in the polyether polymer may all bepolymerizable functional groups, nonpolymerizable functional groups, orboth.

The average molecular weight (Mw) of a polyether polymer is notespecially limited, but it is usually about 500 and 2 million, andadvantageously about 1,000 up to 1.5 million.

The polymers of these preferred families are also advantageouslyselected from polymers which are crosslinkable by ultraviolet, infrared,heat treatment and/or electron beam (EBeam).

When a protective layer is intended to form the collector of the anode,it consists or consists essentially of an electron-conducting material.The electron-conducting material may be of metal, selected from Ni, Cuand stainless steel.

A metal protective layer may be obtained by a physical or chemical vapordeposition method, preferably with a thickness of 100 to 150 Å. It mayalso be obtained from a free metal strip, preferably having a thicknessof 10 to 15 μm.

Preferably, a metal protective layer has a surface resistivity lowerthan 1 Ω/cm².

A second object of the invention relates to the multilayer materialobtained by the inventive method.

A multilayer material according to the invention comprises at least onelayer of active lithium and one protective layer adhering to oneanother, characterized in that the lithium layer is a layer of activelithium which carries, on at least one of its surfaces, a continuous ordiscontinuous passivation layer having an average thickness of less than50 Å, and in that said at least one protective layer consists orconsists essentially of an ion-conducting material.

When the multilayer material is intended to form a two-sided anode of anelectrochemical battery, the two surfaces of the layer of active lithiumcarry an ion-conducting protective layer. The two protective layers mayconsist or consists essentially of the same material or of differentmaterials.

When the multilayer material is intended to form a one-sided anode of anelectrochemical battery, one of the surfaces of the layer of activelithium adheres to a protective layer consisting or consistingessentially of an ion-conducting material, and the other surface of thelayer of active lithium adheres to a protective layer consisting orconsisting essentially of an electron conducting material.

In a multilayer material obtained by the inventive method, theadhesiveness between the lithium layer and the protective layer,measured by the method ASTM No. D3359, is higher than 4, on a scale from1 to 5.

The protective layers prevent the exposure to an atmosphere from causingthe formation or growth of a lithium passivation layer.

A multilayer material consisting or consisting essentially of a layer ofactive lithium between two metal protective layers preferably has anapplication in areas other than electrochemical generators.

A third object of the invention relates to an electrochemical batterycomprising at least one cathode, an electrolyte, and at least onemultilayer material of the invention as an anode. The multilayermaterial of the invention may advantageously be incorporated in varioustypes of electrochemical battery.

The battery may be a one-sided battery or a two-sided battery. Thebattery may be in the form of an all-solid battery, a liquid electrolytebattery or a gel electrolyte battery.

A one-sided battery comprises at least one assembly comprising thefollowing elements, in the order indicated:

-   -   a collector;    -   a cathode material;    -   a polymer electrolyte, or a separator impregnated with a gel        electrolyte or a separator impregnated with a liquid        electrolyte;    -   a multilayer material;        said multilayer material comprises a layer of active lithium        between a metal protective layer and a nonmetallic protective        layer, consisting or consisting essentially of a material        selected from ceramics of the LIPON type, ionic glasses,        conducting polymers, polymers containing ceramic fillers, and        polymers made conducting by the addition of a solution of an        ionic compound in a liquid solvent, the nonmetallic protective        layer being in contact with the electrolyte.

A two-sided battery comprises at least one assembly comprising thefollowing elements, in the order indicated:

a collector;

a cathode material;

a polymer electrolyte;

a multilayer material;

an electrolyte;

a cathode;

a collector;

said multilayer material comprises a layer of lithium between twoprotective layers, each consisting or consisting essentially of,independently of one another, a material selected from LIPON, ionicglasses, conducting polymers and polymers containing ceramic fillers,and polymers made conducting by the addition of a solution of an ioniccompound in a liquid solvent.

The electrolyte of a battery according to the invention may be a polymerelectrolyte, a separator impregnated with a gel electrolyte, or aseparator impregnated with a liquid electrolyte.

The cathode of a battery according to the invention consists or consistsessentially of a material which comprises an active cathode material,and/or an electron conductor and/or a polymer, and/or a lithium saltand/or a binder.

The active material of the cathode may be selected from LiV₃O₈, V₂O₅,LiCoO₂, LiMn₂O₄, LiMn₁₃Co_(1/3)Mn_(1/3)O₂, and mixtures thereof.

The polymer is preferably a polyether.

The electron conductor consists of Ketjen carbon, Shawinigan carbon,graphite, carbon fibers, vapor-deposited carbon fibers, and mixtures ofat least two thereof.

The lithium salt is preferably selected from lithiumbis-trifluoromethanesulfonylimide (LiTFSI), lithiumbis-fluorosulfonylimide (LiFSI), lithium dicyanotriazole (LiDCTA),lithium bis-pentafluoroethanesulfonylimide (LiBETI), LiPF₆, LiBF₄,LiBOB, and mixtures thereof.

The binder is preferably selected from the group consisting of PVDF,PTFE, and water soluble binders (WSB), such as a SBR rubber for example.

The collector of the cathode preferably consists or consists essentiallyof aluminum optionally coated with carbon.

In an advantageous embodiment, the anode of the generator according tothe invention is a multilayer material which has a metal protectivelayer, consisting or consisting essentially of Ni or Cu, this protectivelayer forming the collector of the anode.

When the lithium film of the multilayer is in contact with a nickel orcopper support, said support serves as a current collector. Theelectrolyte of a generator according to the invention may be a liquid orgel electrolyte which impregnates a separator consisting of apolypropylene (PP) or a sequenced copolymer of polypropylene andethylene (PP-PE-PP).

The gel electrolyte may be obtained from a composition comprising atleast one polymer having crosslinkable groups, at least one lithium saltor at least one liquid solvent and at least one crosslinking agent. Thepolymer is advantageously a polyether or a mixture of four-branchedpolyethers or polyethylene glycol, preferably having an averagemolecular weight MW of between 2,000 and 10,000, more particularlybetween 2,500 and 8,000. The lithium salt may be selected from thosementioned above for the cathode material. The liquid solvent is a polaraprotic solvent selected from ethyl carbonate (EC), propylene carbonate(PC), dimethyl carbonate (DMC), methyl and ethyl carbonate (EMC),diethyl carbonate (DEC), γ-butyrolactone (GBL), vinyl carbonate (VC) andfrom molten salts having a SP lower than 50 Å, and mixtures thereof.

A fourth object of the invention relates to a method for preparing abattery of which the anode is made from active lithium, using amultilayer material of the invention as the anode material.

A generator according to the invention can be prepared by depositing alayer of glass or ceramic adjacent to a layer of active lithium, on ahalf-cell consisting or consisting essentially of a cathode film and anelectrolyte film.

When the electrolyte of a generator according to the invention is apolymer gel electrolyte, a crosslinkable polymer is preferably used, andit is crosslinked by UV, IR or electron beam irradiation, or by heatingor by a combination of both, after having deposited it on a substrate.The crosslinkable polymer may be selected from crosslinkable polymersdefined for the material constituting the protective layer. It isparticularly advantageous to carry out the crosslinkage within thegenerator, after having sealed it.

DESCRIPTION OF PREFERENTIAL EMBODIMENTS OF THE INVENTION All-SolidBattery

For preparing an all-solid battery, a layer of ceramic (constituting theprotective layer) is deposited on a substrate consisting of a half-cell,by plasma sputtering (including nitrogen gases) from a source of LIPON(lithium-phosphorus-nitrogen) prepared by the method described in NewPower Source, PV 2000-03, by K Zaghib and Surampudi, pages 16 to 30 andpages 70 to 80. The half-cell comprises a cathode and a solid polymerelectrolyte (SPE).

The LIPON layer deposited advantageously has a thickness of about 1 μm.The half-cell consists of the superimposition of a collector, a cathodeforming material, and the SPE electrolyte. The protective layer isdeposited on the SPE layer of the half-cell.

The cathode material consists of an active cathode material (for exampleLiV₃O₈), a binder and optionally a material imparting ion conduction anda material imparting electron conduction. The binder may be a polymer ofthe polyether type. The material imparting ion conduction is a lithiumsalt, for example LiTFSI. The material imparting electron conductivitymay be a high specific surface area carbon. The cathode has a thicknessof 45 μm.

The SPE electrolyte consists of a solution of LiTFSi in a polyether typeof polymer, and its thickness is advantageously between 20 and 30 μm. Afilm of lithium is then deposited on the LIPON film. The startinglithium is a commercial extruded film 250 μm thick, which has apassivation layer more than 50 Å thick.

This lithium film is laminated between two stainless steel rolls in aClass 1,000 type anhydrous chamber, to obtain a 50 μm thick film oflithium. The rolling is preferably carried out in the presence of alubricant and/or an additive preferably selected from those described inCA-A-2 099 526.

This 50 μm thick film is actively deposited on the SPE surface, that isvery rapidly and before the lithium is passivated by the air. Thedeposition is preferably carried out in less than 2 seconds.

It has thus been discovered that, if this operating mode is carried outin a predefined time, it unexpectedly avoids the rapid growth of thepassivation film, which is generally formed of lithium carbonate Li₂CO₃and oxide Li₂O and LiOH, and it provides a very strong adhesiveness ofthe layer of active lithium to the protective layer.

The deposition of active lithium on the LIPON, by the method of theinvention, thereby serves to minimize the thicknesses of the Li₂CO₃ andLi₂O layers, thereby substantially improving the long-term cyclabilityof the all-solid battery. By thus lowering the impedance of the battery,excellent performance is obtained, particularly in use with highcurrents.

The deposition of the film of active lithium on the LIPON layer resultsin the inhibition of the formation of dendrites thanks to the presenceof the hard and solid layer of LIPON on the lithium.

Liquid Electrolyte Battery

A liquid electrolyte battery according to the invention comprises acathode, a separator impregnated with an electrolyte, a protectivelayer, and an anode consisting of a film of active lithium.

The cathode may be made from a composite, similar to the one describedfor the all-solid battery.

The separator may be made from polypropylene (PP) or a PP-PPE-PP forexample of the CELGARD type.

The electrolyte is advantageously a solution of lithium salt (forexample LiTFSI) in a solvent (for example a mixture of ethylenecarbonate and diethylene carbonate).

The film of active lithium is obtained by laminating a film ofcommercial lithium.

For assembling a battery, the LIPON film is deposited on one of thefaces of the separator by cathode sputtering, the active lithium israpidly deposited on the free-face of the LIPON, and a film of cathodematerial is then deposited on the free face of the separator.

Gel Electrolyte Battery

According to this particular embodiment of the invention, a cathode isfabricated from a composition prepared by mixing 82% of LiFePO₄(produced by Phostech) with 3% by weight of Ketjen black, 3% ofgraphite, 12% of PVDF in the presence of the solvent NMP, at the rate of20% by weight, of the total weight of the powders previously mixed.

The solution is spread on an aluminum carbon collector, and the solventis evaporated. A film is obtained having a thickness of 45 microns, witha porosity of 73%. The cathode is calendered until a porosity of 40% isobtained.

A ceramic film of the LIPON type having a thickness of 1 μm is depositedon a film of Celgard 3501®, and a film of active lithium is thendeposited on the free surface of the LIPON film, by lamination of anextruded lithium.

The cathode is then deposited on the free face of the Celgard 3501®film.

The assembly thus produced is introduced into a flexible aluminum bag,together with a mixture of precursors of the gel electrolyte, and thebag is then sealed. The mixture of precursors consists of 95% by weightof a polyether (which is preferably of the four-branched type), amixture of 1 M LiTFSi+0.5 M LiPF₆+EC+GBL (1:3 by volume), and 1,000 ppmof Pekadox 16® as crosslinkage initiator.

The battery was sealed by the technique described in WO2004/068610relative to a rechargeable electrochemical generator, and moreparticularly in example 2 of the document.

The battery is maintained at 60° C. for one hour. This step is necessaryto form the gel in the pores present on the surface of the electrodematerial, of the Celgard and in the LIPON pores. The batteries preparedby implementing this method are functional at ambient temperature.

It has been found unexpectedly that lithium, owing to its particularchemical reactivity, develops an excellent adhesion with glasses andceramics immediately after its lamination.

EXAMPLES

The examples below are provided for illustration and are nonlimiting forthe object of the invention.

Example 1

A half-cell is prepared consisting of a current collector, a cathodematerial and a solid polymer electrolyte SPE.

The cathode material consists of LiV₃O₈, a polyether binder, LiTFSI anda high specific surface area carbon. The cathode has a thickness of 45μm.

The electrolyte SPE consists of a solution of LiTFSi in a polyether typeof polymer, and its thickness is between 20 and 30 μm.

A film of metal lithium having a thickness of 250 μm is obtained byextrusion, and then manually laminated with a jeweler's roll mill for 2seconds. A lithium film having a thickness of 55 μm is thus obtained,with a passivation film on its furnace of which the thickness is 25 Å.

This film is extremely sticky and adheres to the assembly on theLiV₃O₈/SPE cell. The half-cell has an impedance of 6Ω, which is muchlower, hence more advantageous, than the impedance of 12Ω of a cellcontaining a standard lithium film at the same measurement temperatureof 60° C.

Example 2

A film of methyl lithium having a thickness of 250 μm is obtained byextrusion. It is then laminated with a jeweler's roll mill, at ambienttemperature for 2 seconds. A film of active lithium, having a thicknessof 55 μm, is thus obtained, and it has a passivation layer having athickness of 45 Å. This film was evaluated on the same day in an XPSanalyzer. The thickness measured for the Li₂O layer is 255 Å.

A film of active lithium which remained for one week in an anhydrouschamber has a Li₂O layer having a thickness of 250 Å and a Li₂CO₃ layerhaving a thickness of 125 Å.

These values should be compared with those of the commercial lithiumfrom FMC, in which the Li₂O layer has a thickness of 400 Å and theLi₂CO₃ has a thickness of 150 μm.

Example 3

A half-current collector/cathode material/SPE cell is prepared by themethod of example 1.

A LIPON layer is deposited by sputtering on the SPE face of thehalf-cell, from a Li₃PO₄ target. It has a thickness of 900 nm and anadhesiveness, measured by ASTM method number D3359, of 5/5.

Example 4

A LiV₃O₈/SPE/LIPON/lithium type battery was prepared by the followingprocess.

On the SPE face of a half-cell “current collector/cathode material/SPE”prepared by the procedure in example 1, a layer of LIPON having athickness of 1 μm was deposited by cathode sputtering.

A film of lithium was then deposited on the LIPON film, from acommercial extruded film having a thickness of 250 μm, and which has apassivation layer more than 50 Å thick. This film of commercial lithiumwas laminated between two stainless steel rolls in a Class 1,000 typeanhydrous chamber, to obtain a 50 μm thick lithium film.

This 50 μm thick film was actively deposited on the SPE surface, in lessthan 2 seconds, and a current collector was then deposited on thelithium film.

The battery thereby produced has a capacitance of 5 mAh. It was cycledin C/3 discharge and charged to a constant potential of 3.1 volts for 1hour. The capacitance and coulomb efficiency are stable during the 100cycles. A 3% loss of capacitance is measured after 100 cycles, but thecoulomb efficiency remains between 99.9 and 100%.

A LiV₃O₈/SPE/lithium battery, prepared with a similar half “currentcollector/cathode material/SPE” cell and with a standard lithium, wascycled in C/3 in discharge and charged in 2 C to a constant potential of3.1 volts for 1 hour. After 10 cycles, the capacitance dropped by 30%and the coulomb efficiency by 50%.

In conclusion, the preceding examples demonstrate the very low thicknessof the passivation layer in the multilayer materials of the invention,and the exceptional adhesion of the lithium to its protective layer.

Furthermore, the batteries incorporating a multilayer material of theinvention are characterized by a low impedance and by an outstandingcoulomb efficiency in charge/discharge.

Although the present invention has been described with the help ofspecific embodiments, it is understood that several variations andmodifications may be grafted to said practices, and it is the object ofthe present invention to cover such modifications, uses or adaptationsof the present invention, generally following the principles of theinvention and including any alternative to the present description whichbecomes known or conventional in the field of activity in which thepresent invention applies, and which may be applied to the essentialelements mentioned above, in agreement with the scope of the followingclaims.

1-48. (canceled)
 49. A method for preparing a multilayer material whichcomprises at least one layer of active lithium, said method comprising astep of depositing a film of active lithium on a protective layer at asufficient speed so that substantially no oxidation of the lithiumoccurs, and/or during a sufficient time for the adhesion of the lithiumto develop after contact with the protective layer.
 50. The method asclaimed in claim 49, wherein the layer of active lithium consistsessentially of lithium which has a degree of purity higher than 99%, orof a lithium alloy comprising less than 3000 ppm of impurities.
 51. Themethod as claimed in claim 49, wherein the layer of active lithiumcarries on one or each of its surfaces, a passivation layer which issuch that the ratio “thickness of the passivation layer”/“thickness ofthe layer of active lithium” is between 2.10⁻⁵ and 1.10⁻³.
 52. Themethod as claimed in claim 49, wherein the passivation layer comprisesat least one lithium compound from the group consisting of Li₂O, Li₂CO₃,LiOH, and Li₂S₂O₄; wherein the Li₂O, Li₂CO₃ and LiOH are formed in a dryatmosphere.
 53. The method as claimed in claim 49, wherein a protectivelayer is deposited on each of the surfaces of the film of activelithium, the two protective layers consisting essentially of anion-conducting material.
 54. The method as claimed in claim 49, whereinthe film of active lithium is deposited on a protective layer consistingessentially of an ion-conducting material.
 55. The method as claimed inclaim 49, wherein the film of active lithium is deposited on aprotective layer consisting essentially of an ion-conducting materialand a protective layer consisting essentially of an electron-conductingmaterial is deposited on the free surface of the film of active lithium.56. The method as claimed in claim 49, wherein the method is implementedin a dry air atmosphere, in an anhydrous chamber with a dew pointbetween −45 and 55° C. and a relative humidity between 0.7 and 2.2%. 57.The method as claimed in claim 49, wherein the protective layer isdeposited in 1 to 15 seconds.
 58. The method as claimed in claim 49,wherein an ion-conducting protective layer comprises at least twosublayers, consisting essentially of, independently of one another, amaterial which has an ion conduction higher than 10⁻⁴S.cm², and which isselected from ceramics, glasses, polymers, and polymers containing aceramic filler.
 59. The method as claimed in claim 49, wherein thematerial constituting the protective layer consists essentially of aceramic of the nonstoichiometric lithium phosphorus oxynitride type(LIPON).
 60. The method as claimed in claim 49, wherein the protectivelayer consists essentially of a ceramic or of a glass with a thicknessequal to or less than 1 μm, of a solution of an ionic compound in apolymer, of a polymer carrying ionic groups, of a polymer containing aceramic, of a polymer with a thickness between 1 and 100 μm, or of anelectron conducting material.
 61. A multilayer material obtained asclaimed in claim 49, comprising at least one layer of active lithium andone protective layer adhering to one another, wherein the lithium layeris a layer of active lithium which carries, on at least one of itssurfaces, a continuous or discontinuous passivation layer having anaverage thickness of less than 50 Å, and wherein said at least oneprotective layer consists essentially of an ion-conducting material. 62.The multilayer material as claimed in claim 61, wherein the two surfacesof the layer of active lithium carry an ion-conducting protective layer.63. The multilayer material as claimed in claim 61, wherein one of thesurfaces of the layer of active lithium adheres to a protective layerconsisting essentially of an ion-conducting material, and the othersurface of the layer of active lithium adheres to a protective layerconsisting essentially of an electron-conducting material.
 64. Anelectrochemical generator comprising at least one cathode, oneelectrolyte and at least one anode, wherein the anode comprises amultilayer material as claimed in claim
 61. 65. The generator as claimedin claim 64, wherein it comprises at least one assembly comprising thefollowing elements, in the order indicated: a collector; a cathodematerial; a polymer electrolyte, or a separator impregnated with a gelelectrolyte or a separator impregnated with a liquid electrolyte; themultilayer material forming the anode; wherein said multilayer materialcomprises a layer of active lithium between a metal protective layer anda nonmetallic protective layer, consisting essentially of a materialselected from ceramics of the LIPON type, ionic glasses, conductingpolymers, polymers containing ceramic fillers, and polymers madeconducting by the addition of a solution of an ionic compound in aliquid solvent, the nonmetallic protective layer being in contact withthe electrolyte.
 66. The generator as claimed in claim 64, wherein itcomprises at least one assembly comprising the following elements, inthe order indicated: a collector; a cathode material; a polymerelectrolyte; the multilayer material forming the anode; an electrolyte;a cathode; a collector; wherein said multilayer material comprises alayer of lithium between two protective layers, each consistingessentially of, independently of one another, a material selected fromLIPON, ionic glasses, conducting polymers and polymers containingceramic fillers, and polymers made conducting by the addition of asolution of an ionic compound in a liquid solvent.
 67. The generator asclaimed in claim 64, wherein the lithium film of the multilayer is incontact with a nickel or copper support which serves as a currentcollector.